The quantitative study of how fluids (gases and liquids) move.

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Calculating the drag force provided by a laminar flow [duplicate]

If I drop a ball into viscous fluid (e.g. oil), by calculation I know that the fluid flow is laminar. So which equation do I need to calculate the drag force provided by fluid? The drag equation, ...
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Have we figured out how to analyze turbulent fluids?

I was surprised to read that we don't know how to analyze turbulent fluids. On page 3-9 of The Feynman Lectures on Physics (Volume One), Feynman writes: Finally, there is a physical problem that ...
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About turbulence modeling

I have some questions about this paper: Lagrangian/Hamiltonian formalism for description of Navier-Stokes fluids. R. J. Becker. Phys. Rev. Lett. 58 no. 14 (1987), pp. 1419-1422. After reading ...
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What is the critical diameter ratio of a cone shaped reducer before air overflows

Let's assume we have a cone shaped cylindrical reducer with $D_1$ inlet and $D_2$ outlet diameter (funnel). Air flows through it with velocity $v_1$ at inlet and $v_2$ at outlet. With the velocity ...
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What stops giant cruise ships toppling over in rough seas?

A week ago, 2 of the most gigantic cruise ships in the world docked near my city. If you have seen one, or been on one, you will know how large they are. They look extremely unsafe to me, although ...
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How does vasoconstriction/vasodilation of arterioles change blood pressure?

Background: I am coming at this question from an electrical engineering background, and I feel like I am missing certain assumptions that are going into the statement found in my physiology textbook, ...
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Breaking the sound barrier underwater

Theoretically, if I were to launch something faster than the speed of sound in water (around 5 times that of air), what would happen?
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299 views

Why do I sink then float in a swimming pool?

Was swimming this morning and observed something strange: if I stop treading water, hold my legs together, arms pressed against my sides, then I sink to about 3m below the surface, and then rise again ...
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104 views

Could a Jumbo Jet aircraft fly on paper wings?

My dad was an airline pilot and, during his training, his instructor told him that, in absolutely ideal conditions, (in practice obviously impossible) that the actual material composing the wing ...
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125 views

9-point stencil “equivalent” for advection equation

So I inherited from some people a code that solves the advection-diffusion-reaction equation for a particular system. The original code was first implemented in 1D which worked fine in cartesian ...
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70 views

Landau's Ideal fluild one dimentional flow equation

There is a similar Phys.SE question here, but I still didn't get the idea. The problem is: Write down the equations for one-dimensional motion of an ideal fluid in terms of the variables $a$ and ...
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157 views

What is the cause for turbulence?

The transition from laminar flow to turbulent flow is usually told interms of Reynolds numbers. The Reynolds number is $Re=UL/\nu$ where $U$ is the speed, $L$ is dimensional length and $\nu$ is the ...
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No diffusion term in conservation of mass in Navier-Stokes equations?

I have followed derivations of the Navier-Stokes equations and I can see how the various terms arise in the "main equation", the momentum conservation equation. However I don't understand why the ...
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Viscosity, bubbles and (super)fluids

3-part question, but I think it's simple enough... Does the tendency for cavitation in a fluid depend on its viscosity? If so what does this imply for superfluids, having 0 viscosity? And for that ...
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Pressure gradient - derivation for air stream

I need help clarifying the statement made here that $$dp = l\frac{dp}{dx}$$ $\frac{dp}{dx}$ is an infinitely small change in pressure at some point x. $dp$ is the total change in pressure between ...
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51 views

Why is there a pressure drop across a Kaplan turbine?

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes its static pressure as it moves through the turbine and gives up energy. But how does this pressure ...
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110 views

How does fluid velocity affect the dissolution of some solute in the fluid?

Suppose we have a perfect sphere of some solute such as sugar and we place it in a fluid such as water, at a certain temperature, that is not moving. It will dissolve and diffuse into the water due to ...
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218 views

When an object plunges into water, what is the maximum height a droplet from splash can reach?

I cleaned up the kitty litter just some minutes ago. When I threw the products of our 7kg cat into the toilet bowl, the broth splashed and one drop went straight into my eye. yuk. Here come the ...
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134 views

What's wrong with this argument that aerodynamic lift really does rely on Bernoulli? [duplicate]

There is a grade-school explanation of how a wing works that goes approximately like this (although I'm leaving out an erroneous bit): Because of the geometry of the way the wing meets the air, ...
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Slow sustained liquid movement in a vacuum

Can water or any other liquid be made to “simmer” or “low boil” (slow sustained liquid movement) in a vacuum as opposed to go from liquid to all out boil when the vapor pressure is equal to the ...
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398 views

How does the area of an open window affect airflow?

This question stems from a disagreement between me and my girlfriend. During the hot summer months, we like to open up the windows during the early morning to cool down our flat a bit. One of us ...
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45 views

What is the Proper way to determine overall velocity in a pipe?

I am running a simulation of fluid in a pipe. The fluid in this pipe is "swirling" (instead of just moving in one direction, it's rotating as well. Like the Helix below. The fluid is faster on the ...
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886 views

What is the cause of the surface tension of the liquids? [duplicate]

What is the cause of the surface tension of the liquids? How to know the direction of tension force on the free surface of the liquid? I know that the surface tension is the force acting normally ...
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Sriarcha, Shampoo and Unexpected Trajectories

Some time last year my parents-in-law related to me a story which rang true in my scientific brain. They had gone out to see a show, and then decided to go to a fancy Asian restaurant. One course ...
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102 views

What is the maximum speed of an object moving trough air? [closed]

While seeing the comic Flash I wondered what could be the maximum speed of a invulnerable human being (like Allen) running through air on the surface of the Earth? At what speed would its surrounding ...
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108 views

Will the water go inside the moving water bottle?

Let's say that there is a empty bottle in the water moving at a high speed like this: My question is: Will the water go inside the the empty bottle when the bottle is moving at a high speed? If ...
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418 views

Orifice Jet Flow experiment

I am writing up a report on Orifice jet flow experiment in which I am required to find coefficient of flow velocity, $C_v$, and the Coefficient of discharge, $C_d$. There are couple of things that I ...
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Measurement of compressible flow velocity

Assume that you have a pipe with known volume fow rate $\dot{V}_1$ and pressure $p_1$ on the first point. You use an ideal gas as fluid. We derived in our script a formula for the case that you ...
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How to calculate pressure loss due to water leakage from a hole in a pressurized unit

I am trying to develop a method for calculting the rate of pressure loss from a small hole in a pressurized vessel full of water (small air pocket likely at top of vessel). I've found a formula for ...
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2D aerofoil fluid analysis - find velocity ratio

I just wondered if you could help me out on this fluid mechanics question? I have worked through it myself but am very unsure of my answer (not yet found the pressure difference) the question is ...
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238 views

Is there a simple equivalent to Ohm's law for gas (pressure=R*throughput)?

Question I have the feeling gas cannot have an equivalent of Ohm's law, tying pressure and throughput via some kind of fluid resistance constant depending on the geometry of the obstacle considered. ...
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40 views

drift velocity of gas needed to get into a pressurised vessel

Would a gas entering a narrow tubular opening of an initially empty vessel at a given velocity, fill up the vessel to a definite pressure? If so, how is the velocity of the gas related to the final ...
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Cosmology: collisionless vs collisional fluids?

I try to understand the difference between collisionless and collisional fluids in cosmology. My first question is the following. In the context of FLRW cosmology, we suppose that the Universe can ...
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Why do ice cubes stick together or to the edges of a drinking glass?

I was drinking iced-water from a drinking glass (made of glass) at a restaurant yesterday when I was taking a drink, I noticed that there is very little ice water coming out and then suddenly, the ice ...
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Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies. Given that, why is pitting not used on motor vehicles?
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Self Stirring Boiling Liquid

A couple of weeks ago, a friend and I were brewing a new batch of beer. We boil our wort in a turkey fryer. Pretty standard setup for beginners. Anyway, our wort was getting pretty close to boiling ...
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Does a venturi injector contradict the 2nd law of thermodynamics?

The picture below shows a venturi injector. When the water flow enters the narrower cross section its velocity increases and its pressure decreases. Subsequently, fluid is sucked (or injected) into ...
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What granular/colored material suspends itself in an enclosed container filled with water regardless of pressure, gravity and buoyancy?

i've been looking around for an answer but it turns out that google dsn't think it's an obvious question. Would really appreciate the help. Basically i'm wondering if there is any known material that ...
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120 views

What is the best way to calculate speeds at other points in a venturi-tube when knowing one?

I and a friend have made a venturi tube trough which water flows at a low speed. The flow is therefore laminar. We measured the static pressure using some piëzometers at the points 1,2 and 3. We know ...
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Fluids Dynamics - Transmission Oil Dilution Problem [closed]

I have a fluids dynamics (I guess) problem with my car and I can't seem to find the answer: I have to change my transmission oil. It has a 7 liter total capacity, but due to the torque converter, I ...
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238 views

Bubble in a pipeline

I am just thinking about this phenomenon: We have a horizontal pipeline with a flowing liquid, which contains a small bubble of gas. How do the dimensions of this bubble change when it reaches a ...
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1answer
46 views

Water well fluid dynamics [closed]

In my home village everyone has their own water well at the foot of the mountain (limestone) . The wells are over 100 feet deep but they are not cemented or have the area between the hole and the ...
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Symmetry considerations in Plane Poiseuille Flow

I'm taking a first course on fluid dynamics, and I have this (sort of) conceptual question that's been nagging me for a moment now. I can completely follow the mathematics behind the derivation of the ...
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Why is pressure in a liquid the same in all directions?

I'd like answers both in the more intuitive side an on the more precise side. Thinking of water as "cubes" of water, for example, would allow pressure in the z axis to be independent of the y or x ...
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How does a Venturi Injector comply with energy conservation?

How does a Venturi Injector comply with energy conservation? When the water flow enters the narrower cross section its velocity increases and its pressure decreases. When the pressure gets lower ...
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Is this a case of the “venturi effect”? What's behind the “Venturi effect” actually?

Some dinghy sailboats have a hole in the bottom of their deck used to automatically bail out water after a capsize. bailer of the laser sailoat The mechanism only works if the boat is moving. The ...
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Would a solution to the Navier-Stokes Millennium Problem have any practical consequences?

I know the problem is especially of interest to mathematicians, but I was wondering if a solution to the problem would have any practical consequences. Upon request: this is the official problem ...
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Alternative to Naphthalene Sublimation

I work in a wind tunnel that uses Naphthalene for flow visualization. Specifically we use it to see the location of transition from laminar to turbulent flow. We mix it with acetone and spray it on ...
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How do I calculate the energy balance of a trompe?

I was quite fascinated by the concept of an ancient type of air compressor, called a trompe. It entrains air bubbles into a falling stream of water via the Venturi effect, and extracts the air at a ...
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Why do turbine engines work?

I know roughly how a turbine engine (let's say a gas turbine producing no jet thrust) is supposed to work: The compressor forces fresh air into a combustion chamber, where it reacts with fuel to ...